merge https://github.com/clamsproject/app-nlp-example

[keighrim]

https://github.com/clamsproject/app-nlp-example holds a little bit old app development guide and app usage guide with a concrete example code. As discussed in https://github.com/clamsproject/app-nlp-example/issues/8 , we'd like to merge the contents from that repository into

1. developer's manual at https://github.com/clamsproject/clams-python/tree/develop/documentation , specifically
   1. introduction.rst
      1. input-output.rst
2. inline comments in the development template at https://github.com/clamsproject/clams-python/tree/develop/clams/develop/templates/app , specifically,
   1. README.md
   2. app.py
   3. metadata.py
   4. Containerfile
3. user manual at https://github.com/clamsproject/apps/blob/main/docs/clamsapp.md

[keighrim]

Also, in the clams-python's documentation, there's tutorial.rst, that can be a good place for migrating lots of code from the nlpexample.